Switch from print to logging

[williamFalcon]

Use logging instead of print. (@Ir1d you brought this up before)

Suggested by @adefazio

[humandotlearning]

hey @williamFalcon could you just guide me to the files that needs print to be changed to logging and i'll do it. Thanks.

[Borda]

I think that we were talking about it already a few months back :] happy to see it pass O:-)
@williamFalcon could you draw what kind of messages should be info and debug?

@humandotlearning please use lazy formating

logging.info('Epoch %05d: %s did not improve', epoch + 1, self.monitor)

see: https://stackoverflow.com/a/52012660/4521646

[Ir1d]

I suppose f-strings are preferred?
should we exposure logger as an option, since I prefer loguru, while others might like something else.

[Ir1d]

Given a second thought, what about adding a info and some debug function into LightningLoggerBase?
Something like: self.logger.info() , and users will be free to use whatever logger they like by specifying in custom logger.

However: after a quick search. their are certain functions which dont have access to LoggerBase at this moment. For example the callback

[williamFalcon]

Please use f-strings!

[humandotlearning]

okay as @williamFalcon suggested i'll go with f-string. I have done a performance comparison if anyone is interested.
https://colab.research.google.com/drive/1J6-SFq5nDGTYDH7GIpzixbjYS0UvZ30E

[Borda]

@humandotlearning @lr1d already started in #457

[Ir1d]

actually I'm stuck with how to let users select custom printing function? Any idea on this?

[Borda]

@Ir1d what do you mean by custom printing function? logging.info/debug/warning / print()... ?

[Ir1d]

@Borda I mean using other libraries such as loguru. But yes, what if someone wants to use debug/warning or other stuffs

[Borda]

it is nice library, but I would follow the same strategy as for PyTorch, do not include anything extra until it is really needed so I would sta just with the standard logging , @williamFalcon ?

[Borda]

@williamFalcon @Ir1d just noticed that using f-string makes unable to use python 3.5 and lower...
https://www.reddit.com/r/Python/comments/5xswh9/can_you_import_fstrings_in_python_35/
https://stackoverflow.com/questions/55182209/f-string-invalid-syntax-in-python-3-5

[Ir1d]

@Borda Yes, and I believe @williamFalcon is aware of this fact 😂

[ethanjperez]

It's possible to use f2format to convert f-strings to str.format, to be compatible with Python <=3.5

[williamFalcon]

@ethanjperez amazing haha. it’s finally happening :)

i think it’s a good place to start for a PR @ethanjperez ?

[Borda]

@ethanjperez it is true, but I am not sure that we do not want to have this "".format() formatting...
it works exactly as it is written in the package description:

# the original code
var = f'foo{(1+2)*3:>5}bar{"a", "b"!r}boo'
# after `f2format`
var = 'foo{:>5}bar{!r}boo'.format((1+2)*3, ("a", "b"))

@williamFalcon ^^